Plasma arc torches are widely used in the heating, cutting, gouging and marking of materials. A plasma torch generally includes an electrode, a nozzle having a central exit orifice mounted within a torch body, electrical connections, passages for cooling, and passages for arc control fluids (e.g., plasma gas). Optionally, a swirl ring is employed to control fluid flow patterns in the plasma chamber formed between the electrode and nozzle. In some torches, a retaining cap can be used to maintain the nozzle and/or swirl ring in the plasma arc torch. In operation, the torch produces a plasma arc, which is a constricted jet of an ionized gas with high temperature and high momentum.
Consumables of a plasma arc torch are susceptible to failures. The life of consumables can fluctuate randomly depending on numerous controllable and uncontrollable factors. The ability to detect the end of consumable life or consumable failures can provide many benefits including reducing the need for operator attention by increasing automation opportunities, reducing cutting machine idle time by reducing consumable inspection, increasing effective life of consumables by reducing premature consumable change-out, increasing productivity by reducing possibility of mid-cut consumable failure, and reducing damages to other components caused by a consumable failure.
An exemplary consumable failure occurs when the tip of an electrode of a plasma arc torch, including the emitter of the torch, is molten and blown away as a result of erosion of the hafnium on the electrode. Consequently, the electrode body can no longer hold the tip in place. During this event, the heat load to the torch and the consumables increases dramatically because the arc is now in direct contact with the electrode body, the nozzle, and possibly the shield. Therefore, if the arc is not timely shut off, the heat can damage other torch components, such as the swirl ring, the shield, the retaining cap, and eventually the plasma arc torch itself. In addition to the absence of an emitter in an electrode, other consumable failures include a large loss of consumable material or a plasma arc emitting off of a part of an electrode other than the emitter.
Consumable failures can also occur when incorrect consumables are installed in a plasma arc torch during a torch operation. An exemplary plasma arc torch can be operated at several different current levels, for example, 65 Amps, 85 Amps or 105 Amps. When the plasma arc torch operates at 105 Amps, it requires a higher flow rate than during operation at 65 Amps. Due to the varying cooling flow and/or shield flow rates that are required to operate the plasma arc torch at different current levels, different consumables are needed for operation at each current level. Furthermore, different consumables may be needed when other operating parameters of the torch are adjusted, for example, amperage, material type or application.